Combustion apparatus



Aug. 25, 1959 G. BROLA 2,901,032

COMBUSTION APPARATUS Filed Nov. 22, 1955 INVEN'I'OR GABRIEL BRO Y ATTORNEY United States Patent COMBUSTION APPARATUS Gabriel Brola, Bourg La Reine (Seine), France, assignor' to Soci't Anonyme dite: Generale Thermique-Procedes Brola, Le Pre Saint Gervais, France Application November 22, 1955, Serial No. 548,491 Claims priority, application France November 24, 1954 2 Claims. (11. 158-76) This invention relates to combustion apparatus of kind usable in connection with various thermal installations in which it is required to generate and maintain combustion gases at an elevated temperature, such as gas turbines, steam generators, space heating units, furnaces, and the like.

An object of the invention is to provide an improved form of combustion chamber which will be capable of developing high amounts of heat for a given volume. The quantity of heat developed per unit sectional area of a combustion chamber is substantially proportional to the volume of the combustion gases therein, or otherwise stated, to the product of the combustion rate and the total area of the flame front of the combustion gases. Objects of the invention, accordingly, are to increase both the rate of combustion and the flame front area in order to increase the amount of generated heat. Further objects are to provide improved combustion apparatus in which the fuel injecting and ignition means are located outside the combustion chamber and are hence protected from the high temperatures prevailing therein. Further objects are to preheat the combustion air, increase the combustion temperature, and promote the cooling of the walls of the combustion apparatus, using forthis purpose the simultaneous effects of combustion airflow, radiation, and conductivity effects. Further objects will appear as the description proceeds.

According to the principal aspect of the invention,.improved combustion apparatus comprises a concave shell member, means for discharging fuel and air into said shell member and for ignition of said fuel, means defining an annular wall coaxial with the shell member and spaced from the periphery thereof, and a plurality of angularly spaced finlike elements interconnecting the shell periphery with said annular wall and defining auxiliary air inlet passages between said elements.

The shell member may be formed with an axial main air inlet aperture having reentrant side walls defining a convergent inlet nozzle for imparting a high velocity of flow to the primary air entering the chamber through said inlet. The fuel is injected axially of this inlet, and the rfuel injector nozzle and associated ignition device can thus be located outside the chamber due in particular to the high flow velocity, whereby the flame is prevented from moving back toward the injector nozzle outlet. The shell is formed with space ports therein for supplying secondary air, and these ports are preferably likewise formed with an inwardly convergent shape. The fin-like elements are preferably formed with concave base surfaces directed towards the common axis of .the shell member and the annular wall member to receive and partly reflect back heat radiated therefrom, and said elements taper outwards into the auxiliary airflow, which sweeps past the extensive side walls of said elements, there promoting eflicient withdrawal both of the part of said radiated heat absorbed by the fins, and of the heat transferred to said fins from the shell member by conductivity. Owing to this arrangement the tempera- 2 ture of the combustion gases is. increased by reflected radiation from the base surfaces of the fins, and simultaneously the fins and other wall portions of the apparatus are effectively cooled and the combustion air-flow is preheated.

The fin-like elements of the invention have another important function. When correctly shaped in a manner later describd in detail, they are found to create a number of vortices in alternate directions, which exert a stabilizing action on the flame front and impart to it a wavy or undulating configuration in cross section that serves greatly to increase its effective surface area, as compared to the usual cylindrical or flat or part-spherical flame front pattern obtained in conventional combustion chambers. Increasing the flame front area, as previously indicated herein, .acts to increase the quantity of heat evolved by a chamber of given size.

The rate of combustion is also increased as a result of the energetic pre-heating of the carburized mixture by the walls of the shell, which reduces the time required to vaporizethe fuel droplets and hence the time required for the entire mass of fuel in a given period to reach a state of ignition. Increase of the combustion rate decreases the length of the flame and thus again results in. a decrease in the longitudinal dimension of the chamber required to ensure complete combustion.

The above and further objects and features of the invention will be made clear from the ensuing description, in which one exemplary embodiment of combustion apparatus according to the invention is illustrated with reference to the accompanying drawings, wherein:

Fig. 1 is an axial cross sectional view of the improved combustion apparatus;

Fig. 2 is a cross sectional developed view of the fins thereof;

Fig. 3 is an overhead perspective view of the apparatus;

In the illustrated embodiment, the improved combustion apparatus comprises a concave shell 1 made of any suitable highly-refractory material, and formed with an axial opening 2 around which the shell wall curves inwardly to provide a nozzle-like entrance. The shell 1 may have anysuitable configuration in axial cross section e.g. it may be approximately hemi-spherical or paraboloidal. At spaced points through the wall of the shell there are formed a plurality of ports such as 3, 4, 5 which are preferably provided with flared or chamfered ends outwards of the shell. Formed integrally with or con- .nected to the outer marginal area of the shell member are a set of outwardly projecting fins 6, the outer ends of which are interconnected by a circular annulus or rim 7 having a generally frustoconicalouter surface as shown.

The fins 6 are illustrated in developed cross sectional view in Fig. 2, from which it will be seen that each fin has a generally triangular cross sectional shape in planes generally parallel with the outer conical surface of the rim 7. The apices 8 of the fins, i.e. their upper ends as seen in Fig. 1, are rounded, while their bases 24 i.e. their lower ends according to Fig. 1,. are concave and are defined by sharp edges or apices 9 and 10.

The assembly comprising the shell 1, fins 6 and rim 7 is mounted in the end of a tubular member 12 made of refractory material, with the frustoconical outer surface of the rim 7 seated against a complementary frusto conical surface formed in a thickened end portion 13 of the tubularmember, which defines a throat or restriction substantially on a level with the base of the fins.

The upper end of tubular member 12 is inserted in an aperture formed in one wall of a conduit or casing 25 and is secured therein by any suitable means, so that the outer convex side of the shell 1 projects into the inner space defined between the walls of the member 25, which is arranged for delivery of primary combustion air to the apparatus. Mounted in the opposite wall of the member 25 is a fuel injector nozzle 14 projecting axially towards the entrance aperture 2 into the shell 1, but extending short of said aperture. Also mounted in said wall next to the injection nozzle is an ignition member or sparking plug 15 connected to a suitable source of voltage, and projecting to a point adjacent the outlet of injection nozzle 14 forwardly thereof. The combustion apparatus operates as follows:

Combustion air enters the shell 1 partly through the wide central entrance nozzle 2 and through the ports 3, 4 and 5 to provide the primary and secondary airflow, respectively, and partly through the spaces 11 between thefins 6, as indicated by an arrow in Fig. 1, to provide a tertiary airflow. The primary air drawn in through the central aperture 2 becomes mixed with the pulverized fuel from injection nozzle 14 and immediately forms a combustible charge therewith which is ignited by ignition device 15 before the charge has even penetrated the combustion chamber, in the area of nonturbulent, high-velocity flow determined by the entrance nozzle 2. Owing to the high flow velocity of the combustible charge in this area, the flame front istprevented from moving ba k towards the outlet of the injector nozzle 14. It will be observed that in this arrangement the injection nozzle and ignition device are mounted outside the combustion chamber and are not subjected to the high temperatures developed therein, so that their service life is considerably lengthened. V

Due to the configuration of the inner shell chamber, and particularly due to the reentrant wall portions surrounding the central aperture 2, the partially or wholly ignited charge entering the chamber forms a plurality of high-velocity vortices disposed in an annular array Within the shell 1, somewhat in the manner indicated by the lines 16, thereby promoting an intimate mixing of the burning mixture with any non ignited fuel droplets that may be present, and with the secondary air entering the lateral ports 3, 4, 5. Thus the inner space of the shell 1 becomes filled with a body of gas in substantially uniform combustion which tends to project therefrom into the tubular member 12, where the combustion continues with the additional or tertiary air delivered through the spaces 11 between the fins.

It is found that the flame front becomes stabilized in the area adjacent the bases of the radial fins 6. This is explained by the fact that the air-flow entering through the spaces 11 divides into a plurality of vortices such as 17 (Fig. 2) alternately directed in opposite directions, which act so to speak to catch the flame and bond or stabilize the periphery of the flame front in that area. However, combustion continues at a high rate within the tube 12 so that its side walls are carried by radiation to a high temperature thereby further accelerating the rate of combustion within it, the combustion being completely terminated as the gases issue from the opposite end of the comparatively short tube.

The array of fins 6 shaped as disclosed above perform an important heat exchange function. This is because the comparatively large laterial areas such as 18 and 19 (Fig. 2) of the fins are swept by the cool airflow from the space 25, while the smaller base areas 20 thereof are directly exposed to the radiation from the burning mass, and this radiation effect is enhanced by the concave form imparted to said base areas as stated earlier. Thus the heat supplied to the shell 1 and transferred to the fins by conduction is effectively removed by the cool air sweeping across the sides of the fins, together with the heat transferred to the inner fin surfaces by radiation as mentioned above. An extremely efiicient cooling effect is obtained by the tertiary airflow supplied between the fins. At the same time the airflow is preheated, and the temperature within the space 12 is further increased by reflection from the concave base surfaces of the fins.

It will be understood that many modifications may be made in the single illustrative embodiment described and shown herein without departing from the scope of the invention. 7

What I claim is:

1. In combustion apparatus, the combination of a concave-convex shell member having a centrally located axial air-inlet aperture, an injector nozzle located outside of said shell member at the convex side of the latter and aligned axially with said air-inlet aperture for injecting divided fuel into said shell member through said air inlet aperture, ignition means for igniting the divided fuel issuing from said injector nozzle, said shell member further having openings therein for the admission of secondary air, a finsto-conical annular wall extending coaxially around said shell member and spaced radially from the latter with said annular wall converging in the direction in which said shell member is concave, and a plurality of angularly spaced fin elements extending radially between said shell member and said annular wall to define air-inlet passages for tertiary air between the successive elements, each of said elements being symmetrical about a plane which includes at least one line extending radially with respect to the axis of said shell member, each of said elements increasing in thickness in the direction to-';

ward the end face of the element between the small diameter edge of said annular wall and the edge of said shell member so that said air-inlet passages are convergent in the direction of the flow of the tertiary air therethrough, said small diameter edge of the annular wall extending beyond said edge of the shell member in the axial direction so that said end faces of the fin elements and the passages therebetween are directed toward said axis of the shell member, thereby to direct the flow of tertiary air through said passages toward a combustion zone at the concave side of said shell member while the flow of tertiary air is rendered turbulent upon release from said convergent air-inlet passages at said end faces of the fin elements.

2. In combustion apparatus, the combination as in claim 1; wherein said end faces of the fin elements are concave both to promote the turbulence in the tertiary air admitted through said air-inlet passages and to efficiently radiate heat back to said combustion zone; and wherein each of said fin elements has side faces of relatively large area with respect to the area of the related end face so that the fin elements are efiectively cooled by tertiary air flowing through said air-inlet passages and sweeping across said sides faces. I

References Cited in the file of this patent UNITED STATES PATENTS 1,665,786 Irish Apr. 10, 1928 2,411,181 Altorfer Nov. 19, 1946 2,689,457 Kmppe Sept. 21, 1954 2,693,083 Abbott Nov. 2, 1954 2,701,608 Johnson Feb. 8, 1955 2,725,718 Sheets Dec. 6, 1955 FOREIGN PATENTS 510,584- Canada Mar. 1, 1955 547,338 Germany Mar. 10, 1932 178,351 Switzerland Sept. 16, 1935 

